Edge of the Visible Universe

In the picture

1. 1A nearby galaxy cluster: bright and detailed because its light has had a short journey.
2. 2A middle-distance galaxy cluster: smaller and fainter because its light has traveled farther.
3. 3A far galaxy cluster: barely visible at the limit of arriving light.
4. 4A dark rim at the far edge: the boundary where arriving light fades from view.

Examples

• Seeing lightning before hearing thunder, because sound takes time to arrive.
• Looking at a distant city skyline at night, seeing light that left the buildings earlier.

Quiz: Edge of the Visible Universe (Age 18)

1. 1

   Why can we see only part of the universe?

   • Because some regions of the universe no longer contain any galaxies.
   • Because telescopes are not powerful enough to see every region.
   • Because light from some regions has not had time to reach us yet.
2. 2

   What is true about light from distant objects?

   • It cannot cross empty space.
   • It takes time to travel across space before reaching us.
   • It reaches us instantly.
3. 3

   What limits how much of the universe we can observe?

   • The brightness of the farthest galaxy cluster.
   • The size of the telescope we use.
   • How far light has traveled since it could travel freely.

The answers, each with its explanation, are in the app. This lesson has left the free week, so its quiz is part of the subscription.